I think that is why. Negatives developed with pyro do not work with Cyanotype.

It is not that I have tried a lot, but mine did not work at all, and could not figure out why. Later, Sam Wang mentioned that they do not on alt-mailing-list.

I guess you need to make negatives again.

Warmly,
Tsuyoshi

Well, Sam Wang is a good friend and colleague, and one of the best cyanotype printers in the world, but it is not correct that pyro negatives do not work with cyanotype.

The issues are these. 1) Cyanotype is a very slow process, certainly the slowest of all of the popular altlernative processes. Typically, exposures take at least twice as long with cyanotype as with vandyke. So even if you print with traditional negatives exposures will be very long. And 2) the stain, especially if there is any over-expousure or if the film has a high B+F from age or heat, will add even more time to the exposure, perhaps doubling it.

So, bottom line is that pryo negatives will make great cyanotype prints, but exposure times could be very long.